High substrate temperatures are required to deposit ferroelectric and piezoelectric films of materials such as lead zirconate titanate (PZT) and related derivatives. Such high temperatures prevent the use of conventional photolithography for defining elements of devices.
For example, films of such materials are deposited at high substrate temperatures (by "high" is meant&gt;400.degree. C.) from ceramic or powder pressed targets of the material, such as PZT, using rf magnetron sputtering or ion beam deposition. DC reactive magnetron sputtering is one of the suitable techniques for deposition of such materials with stringent composition/microstructure requirements. Reactive magnetron sputtering offers an excellent control over the rates and pressure of reactants taking part in the reaction, and thereby stoichiometry of the end product. Moreover, the low sputtering gas pressures used in the process enables one to control the film microstructure, purity, and stress density in the films; and absence of the secondary electron bombardment of the substrates allows independent control of the substrate temperature, a critical parameter in the deposition of such multicomponent materials. In addition, due to the high kinetic energy bombardment processes involved in sputter deposition, it is particularly suitable for depositing metastable phases as relatively low temperatures.
Recently, dc magnetron sputtering of a multicomponent target has been used to obtain films of PZT at a substrate temperature of 200.degree. C. with a post-deposition annealing of 550.degree. C. Also, there has been some effort to use a specially designed chamber, with multiple metal targets arranged in an inclined manner, to deposit on a centrally located substrate at elevated temperatures. However, such a chamber needs special designing. Furthermore, the deposition results in unavoidable composition gradients across the film.
Sol-gel techniques, which employs a low temperature process, have been used to deposit thin films of multicomponent oxides. However, in sol-gel deposition, only very thin films (.apprxeq.500 .ANG.) can be spun at a time to avoid microcracks. Hence, the film needs to be built up gradually in steps with intermediate anneals, thus necessitating considerable processing time. Further, the intermittent nature of the growth makes lift-off patterning very cumbersome.
A need remains for the deposition of multicomponent oxide films at ambient substrate temperature.